Ester derivatives of stilbenedicarboxylic acid, such as dimethyl trans-4,4'-stilbenedicarboxylate (DMSDC) and diphenyl trans-4,4'-stilbenedicarboxylate (DPSDC), are useful building blocks for high performance polyester engineering plastics. In particular, a diphenyl ester derivative of stilbenedicarboxylic acid can be transesterified with bisphenol A to form a high molecular weight polyester which is useful as an engineering plastic.
The formation of stilbenes from substituted toluene has been reported by Toland and co-workers (see W. G. Toland, Jr., J. B. Wilkes, and F. J. Brutschy, J. Am. Chem. Soc., 75, 2263 (1953); W. G. Toland, Jr., and J. B. Wilkes, J. Am. Chem. Soc., 76, 307 (1954); U.S. Pat. Nos. 2,610,191; 2,677,703; and 2,688,631).
In these references it was shown that the free carboxylic acid and cyano derivatives of toluene could be converted to stilbenes under particular conditions. It has also been shown that unsubstituted toluene can be converted to stilbene (see Aronstein and Van Nierop, Rec. Trav. Chim., 21, 488 (1902); Friedman, Ber., 49, 277, 1334, 1352, 1551 (1902); and U.S. Pat. No. 3,548,018).
The dimethyl ester derivative of trans 4,4'-stilbenedicarboxylic acid has been reported to have been prepared from methyl p-toluate and sulfur [W. J. Jackson and J. C. Morris, Journal of Applied Polymer Science: Applied Polymer Symposium 41, 307-326 (1985)]; however, the efficacy of efficient removal of hydrogen sulfide and enhancement of yield by careful attention to the high molar ratio of methyl p-toluate to sulfur in this reaction have heretofore been unknown.